1. Field of the Invention
The present invention relates to novel organopolysiloxane compositions useful for the production of silicone elastomers by a so-called polycondensation reaction, and, more especially, to novel "two-component" such organopolysiloxane compositions, namely, organopolysiloxane compositions packaged in two separate packs, one including a crosslinking agent which comprises either:
(i) at least one tri- and/or tetraalkoxysilane, or
(ii) the product of partial hydrolysis of at least one of the alkoxysilanes (i). Prior to actual use of such organopolysiloxane compositions, it is necessary to admix the constituents contained in the two packages and the resulting crosslinking of the total composition thus provided effects production of a silicone elastomer by a polycondensation reaction.
2. Description of the Prior Art
Such organopolysiloxane compositions that can be vulcanized at ambient temperature or, more generally, at temperatures below 60.degree. C. are known to this art. Note particularly French Patent 2,592,657 (see pages 42 et seq.), assigned to the assignee hereof, which describes compositions of this type containing a particular tin catalyst system.
These "two-component" compositions comprise:
(1) a first pack (part No. 1) including at least: PA1 (2) a second pack (part No. 2), sometimes designated a "crosslinking system" , comprising, for example: PA1 (A) an .alpha.,.omega.-dihydroxypolydiorganosiloxane having a viscosity ranging from 50 to 1,000,000 mPa.s at 25.degree. C.; PA1 (B) an inorganic filler material; PA1 (C) a small amount of water; PA1 (D) a crosslinking agent comprising: PA1 (E) a catalytically effective amount of a crosslinking catalyst; and PA1 a hydroretainer comprising an alkali metal acrylate and/or methacrylate group polymer.
(a) an .alpha.,.omega.-dihydroxypolydiorganosiloxane oil or a mixture of such oils of different viscosities; PA2 (b) a filler, typically a pyrogenic and/or precipitated silica, advantageously treated, for example, with hexamethyldisilazane or with octamethylcyclotetrasiloxane; PA2 (c) a small amount of water; and PA2 (d) a crosslinking agent selected from among: PA2 (e) a crosslinking catalyst; PA2 (g) advantageously, a triorganosiloxypolydiorganosiloxane oil and/or an organic plasticizer. PA2 (i) a silane of the formula (R.sup.2).sub.k Si(OR.sup.1).sub.4-k in which the symbols R.sup.1, which may be identical or different, are each a C.sub.1 -C.sub.12 alkyl radical, a halogenated C.sub.1 -C.sub.12 alkyl radical or a C.sub.3 -C.sub.8 alkoxyalkylene radical; the symbol R.sup.2 is a C.sub.1 -C.sub.10 hydrocarbon radical and the symbol k is zero or one, or (ii) a product of partial hydrolysis of such silane (i);
(i) at least one tri- and/or tetraalkoxysilane; PA3 (ii) the product of partial hydrolysis of at least one of the alkoxysilanes (i);
It will be appreciated that the crosslinking agent may be optionally present in part No. 1, but that it is preferably present in part No. 2.
To prepare part No. 1 from its individual components on an industrial scale, the manufacturers generally begin by producing a "dough", that is to say, homogeneously mixing the constituents (a), (b) and (c) described above, while attempting to obtain a mixture (I) containing as much water as possible, this mixture (I) having to be capable of being stored as long as possible (for example for 6 months), depending on the requirements of their customers. However, it has been found that in actual practice it was difficult for this intimate mixture (I) to contain more than 7% by weight of water because the mixture (I) experiences a demixing phenomenon over time, namely, the water in this mixture (I) begins to separate out and float on the top of it. It is then necessary to rehomogenize this mixture (I) mechanically prior to its intended end use.
To produce the part No. 1 described above, in most cases the manufacturers introduce into a mixture (II) containing, for example: a polysiloxane oil (a) described above, optionally containing other fillers such as, for example, ground quartz and a polydiorganosiloxane oil having triorganosiloxy endgroups, the mixture (I) in such amount that the part No. 1 thus obtained generally contains from 500 to 5,000 ppm (parts per million) of water by weight, preferably from 1,000 to 4,000 ppm.
Thus, it is in the manufacturers' interest that the mixture (I) or "dough" described above should contain as much water as possible without the mixture (I) undergoing the water demixing phenomenon during its storage. The formulation of such doughs containing larger amounts of water presents the advantage, for the manufacturers, of permitting the preparation and storage of smaller amounts of these doughs.